His was on an 02 Z06, but anything below 60 degrees and we could not get that car started without killing a battery. I am thinking that you might have had a much lower percentage of ethanol if your Z started right up. We tested the content in my friends car at approximately 79 percent ethanol. As well when we tore things apart this last winter he had the black tar that is sometimes an issue with E85. Just google it you will see. Yes it can be a great fuel, but it does have its headaches as well.
On a side note we did get some of the cold start issues worked out by enriching the cranking fuel enrichment by about 25%, but it still is tempermental below 50 degrees.